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gatieme
@@ -375,7 +375,7 @@ void net_drop_ns(void *p)
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* 网络命名空间定义了2个链表, `pernet_list`和`net_namespace_list`
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`init_net`会被链接到`net_namespace_list`这个双向链表上
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`pernet_operations`结构将被链接到`pernet_list`这个双向链表上
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`pernet_operations`结构将被链接到`first_device = pernet_list`这个双向链表上
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* 如果没自定义网络命名空间的话，所有想用网络命名空间时都将利用默认的`init_net`
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@@ -0,0 +1,489 @@
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进程虚拟地址空间
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=======
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| 日期 | 内核版本 | 架构| 作者 | GitHub| CSDN |
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| ------- |:-------:|:-------:|:-------:|:-------:|:-------:|
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| 2016-06-14 | [Linux-4.7](http://lxr.free-electrons.com/source/?v=4.7) | X86 & arm | [gatieme](http://blog.csdn.net/gatieme) | [LinuxDeviceDrivers](https://github.com/gatieme/LDD-LinuxDeviceDrivers) | [Linux内存管理](http://blog.csdn.net/gatieme/article/category/6225543) |
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#1 网络访问层
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-------
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前面讲述了Linux内核中网络子系统的结构, 现在我们把注意力转向**网络实现的第一层, 即网络访问层**. 该层主要负责在计算机之间传输信息，与网卡的设备驱动程序直接协作.
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本节不会讨论网卡驱动程序的实现和相关的问题, 因为其中采用的方法与第6章的描述仅稍有不同. 本节将详细介绍由各个网卡驱动程序提供、由网络实现代码使用的接口，它们提供了硬件的抽象视图.
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这里根据以太网帧来解释如何在"线上"(on the cable)表示数据，并描述接收到一个分组之后, 将该分组传递到更高层之前，需要完成哪些步骤.
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#2 网络设备的表示
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-------
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在内核中, 每个网络设备都表示为`net_device`结构的一个实例. 在分配并填充该结构的一个实例之后, 必须用`net/core/dev.c`中的`register_netdev`函数将其注册到内核. 该函数完成一些初始化任务, 并将该设备注册到通用设备机制内. 这会创建一个`sysfs`项`/sys/class/net/<device>`, 关联到该设备对应的目录. 如果系统包含一个PCI网卡和一个环回接口设备，则在`/sys/class/net`中有两个对应项:
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##2.1 数据结构
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-------
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在详细讨论`struct net_device`的内容之前, 先阐述一下内核如何跟踪可用的网络设备, 以及如何查找特定的网络设备. 照例. 这些设备不是全局的, 而是按命名空间进行管理的. 回想一下,每个命名空间(`net`实例)中有如下3个机制可用
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* 所有的网络设备都保存在一个单链表中,表头为dev_base
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* 按设备名散列. 辅助函数`dev_get_by_name(struct net * net, const char * name)`根据设备名在该散列表上查找网络设备
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* 按接口索引散列。辅助函数`dev_get_by_index(struct net * net, int ifindex)`根据给定的接口索引查找`net_device`实例. `net_device`结构包含了与特定设备相关的所有信息. 该结构的定义有200多行代码, 是内核中最庞大的结构. 因为该结构中有很多细节,所以,尽管下文给出的版本经过了大量的简化,仍然相当长
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###2.1.1 net_device结构体定义
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-------
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`net_device`结构定义在[`include/linux/netdevice.h, line 1607`](http://lxr.free-electrons.com/source/include/linux/netdevice.h#L1607)
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```cpp
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struct net_device {
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char name[IFNAMSIZ];
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struct hlist_node name_hlist;
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char *ifalias;
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/*
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* I/O specific fields
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* FIXME: Merge these and struct ifmap into one
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*/
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unsigned long mem_end;
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unsigned long mem_start;
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unsigned long base_addr;
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int irq;
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atomic_t carrier_changes;
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/*
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* Some hardware also needs these fields (state,dev_list,
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* napi_list,unreg_list,close_list) but they are not
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* part of the usual set specified in Space.c.
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*/
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unsigned long state;
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struct list_head dev_list;
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struct list_head napi_list;
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struct list_head unreg_list;
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struct list_head close_list;
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struct list_head ptype_all;
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struct list_head ptype_specific;
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struct {
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struct list_head upper;
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struct list_head lower;
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} adj_list;
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struct {
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struct list_head upper;
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struct list_head lower;
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} all_adj_list;
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netdev_features_t features;
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netdev_features_t hw_features;
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netdev_features_t wanted_features;
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netdev_features_t vlan_features;
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netdev_features_t hw_enc_features;
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netdev_features_t mpls_features;
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netdev_features_t gso_partial_features;
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int ifindex;
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int group;
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struct net_device_stats stats;
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atomic_long_t rx_dropped;
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atomic_long_t tx_dropped;
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atomic_long_t rx_nohandler;
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#ifdef CONFIG_WIRELESS_EXT
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const struct iw_handler_def *wireless_handlers;
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struct iw_public_data *wireless_data;
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#endif
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const struct net_device_ops *netdev_ops;
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const struct ethtool_ops *ethtool_ops;
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#ifdef CONFIG_NET_SWITCHDEV
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const struct switchdev_ops *switchdev_ops;
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#endif
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#ifdef CONFIG_NET_L3_MASTER_DEV
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const struct l3mdev_ops *l3mdev_ops;
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#endif
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const struct header_ops *header_ops;
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unsigned int flags;
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unsigned int priv_flags;
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unsigned short gflags;
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unsigned short padded;
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unsigned char operstate;
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unsigned char link_mode;
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unsigned char if_port;
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unsigned char dma;
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unsigned int mtu;
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unsigned short type;
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unsigned short hard_header_len;
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unsigned short needed_headroom;
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unsigned short needed_tailroom;
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/* Interface address info. */
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unsigned char perm_addr[MAX_ADDR_LEN];
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unsigned char addr_assign_type;
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unsigned char addr_len;
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unsigned short neigh_priv_len;
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unsigned short dev_id;
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unsigned short dev_port;
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spinlock_t addr_list_lock;
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unsigned char name_assign_type;
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bool uc_promisc;
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struct netdev_hw_addr_list uc;
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struct netdev_hw_addr_list mc;
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struct netdev_hw_addr_list dev_addrs;
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#ifdef CONFIG_SYSFS
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struct kset *queues_kset;
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#endif
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unsigned int promiscuity;
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unsigned int allmulti;
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/* Protocol-specific pointers */
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#if IS_ENABLED(CONFIG_VLAN_8021Q)
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struct vlan_info __rcu *vlan_info;
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#endif
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#if IS_ENABLED(CONFIG_NET_DSA)
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struct dsa_switch_tree *dsa_ptr;
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#endif
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#if IS_ENABLED(CONFIG_TIPC)
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struct tipc_bearer __rcu *tipc_ptr;
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#endif
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void *atalk_ptr;
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struct in_device __rcu *ip_ptr;
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struct dn_dev __rcu *dn_ptr;
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struct inet6_dev __rcu *ip6_ptr;
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void *ax25_ptr;
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struct wireless_dev *ieee80211_ptr;
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struct wpan_dev *ieee802154_ptr;
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#if IS_ENABLED(CONFIG_MPLS_ROUTING)
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struct mpls_dev __rcu *mpls_ptr;
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#endif
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/*
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* Cache lines mostly used on receive path (including eth_type_trans())
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*/
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unsigned long last_rx;
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/* Interface address info used in eth_type_trans() */
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unsigned char *dev_addr;
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#ifdef CONFIG_SYSFS
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struct netdev_rx_queue *_rx;
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unsigned int num_rx_queues;
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unsigned int real_num_rx_queues;
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#endif
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unsigned long gro_flush_timeout;
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rx_handler_func_t __rcu *rx_handler;
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void __rcu *rx_handler_data;
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#ifdef CONFIG_NET_CLS_ACT
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struct tcf_proto __rcu *ingress_cl_list;
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#endif
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struct netdev_queue __rcu *ingress_queue;
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#ifdef CONFIG_NETFILTER_INGRESS
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struct list_head nf_hooks_ingress;
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#endif
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unsigned char broadcast[MAX_ADDR_LEN];
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#ifdef CONFIG_RFS_ACCEL
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struct cpu_rmap *rx_cpu_rmap;
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#endif
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struct hlist_node index_hlist;
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/*
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* Cache lines mostly used on transmit path
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*/
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struct netdev_queue *_tx ____cacheline_aligned_in_smp;
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unsigned int num_tx_queues;
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unsigned int real_num_tx_queues;
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struct Qdisc *qdisc;
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unsigned long tx_queue_len;
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spinlock_t tx_global_lock;
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int watchdog_timeo;
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#ifdef CONFIG_XPS
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struct xps_dev_maps __rcu *xps_maps;
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#endif
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#ifdef CONFIG_NET_CLS_ACT
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struct tcf_proto __rcu *egress_cl_list;
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#endif
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#ifdef CONFIG_NET_SWITCHDEV
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u32 offload_fwd_mark;
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#endif
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/* These may be needed for future network-power-down code. */
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struct timer_list watchdog_timer;
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int __percpu *pcpu_refcnt;
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struct list_head todo_list;
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struct list_head link_watch_list;
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enum { NETREG_UNINITIALIZED=0,
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NETREG_REGISTERED, /* completed register_netdevice */
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NETREG_UNREGISTERING, /* called unregister_netdevice */
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NETREG_UNREGISTERED, /* completed unregister todo */
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NETREG_RELEASED, /* called free_netdev */
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NETREG_DUMMY, /* dummy device for NAPI poll */
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} reg_state:8;
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bool dismantle;
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enum {
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RTNL_LINK_INITIALIZED,
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RTNL_LINK_INITIALIZING,
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} rtnl_link_state:16;
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void (*destructor)(struct net_device *dev);
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#ifdef CONFIG_NETPOLL
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struct netpoll_info __rcu *npinfo;
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#endif
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possible_net_t nd_net;
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/* mid-layer private */
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union {
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void *ml_priv;
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struct pcpu_lstats __percpu *lstats;
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struct pcpu_sw_netstats __percpu *tstats;
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struct pcpu_dstats __percpu *dstats;
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struct pcpu_vstats __percpu *vstats;
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};
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struct garp_port __rcu *garp_port;
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struct mrp_port __rcu *mrp_port;
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struct device dev;
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const struct attribute_group *sysfs_groups[4];
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const struct attribute_group *sysfs_rx_queue_group;
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const struct rtnl_link_ops *rtnl_link_ops;
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/* for setting kernel sock attribute on TCP connection setup */
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#define GSO_MAX_SIZE 65536
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unsigned int gso_max_size;
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#define GSO_MAX_SEGS 65535
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u16 gso_max_segs;
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#ifdef CONFIG_DCB
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const struct dcbnl_rtnl_ops *dcbnl_ops;
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#endif
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u8 num_tc;
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struct netdev_tc_txq tc_to_txq[TC_MAX_QUEUE];
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u8 prio_tc_map[TC_BITMASK + 1];
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#if IS_ENABLED(CONFIG_FCOE)
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unsigned int fcoe_ddp_xid;
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#endif
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#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)
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struct netprio_map __rcu *priomap;
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#endif
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struct phy_device *phydev;
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struct lock_class_key *qdisc_tx_busylock;
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bool proto_down;
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};
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```
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该结构中出现的缩写`rx`和`tx`会经常用于函数名、变量名和注释中. 二者分别是`Receive`和`Transmit`的缩写,即接收和发送,在以后几节里会反复出现.
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###2.1.2 常见设备类别
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-------
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网络设备的名称存储在`name`中. 它是一个字符串, 末尾的数字用于区分同一类型的多个适配器(如系统有两个以太网卡).
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下表列出了最常见的设备类别
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| 名称 | 设备类别 |
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|:---:|:-------:|
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| ethX | 以太网适配器,无论电缆类型和传输速度如何 |
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| pppX | 通过调制解调器建立的PPP连接 |
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| isdnX | ISDN卡 |
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| atmX | 异步传输模式(asynchronous transfer mode),高速网卡的接口 |
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| lo | 环回(loopback)设备,用于与本地计算机通信 |
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例如, 在使用`ifconfig`设置参数时, 会使用网卡的符号名.
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在内核中, 每个网卡都有唯一索引号, 在注册时动态分配保存在`ifindex`成员中.
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内核提供了[`dev_get_by_name`](http://lxr.free-electrons.com/source/net/core/dev.c?v=4.7#L775)和[`dev_get_by_index`](http://lxr.free-electrons.com/source/net/core/dev.c?v=4.7#L849)函数, 用于根据网卡的名称或索引号来查找其`net_device`实例.
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###2.1.3 设备属性
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-------
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一些结构成员定义了与网络层和网络访问层相关的设备属性.
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| 字段 | 描述 |
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|:---:|:----:|
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| [mtu](http://lxr.free-electrons.com/source/include/linux/netdevice.h?v=4.7#L1691) | (maximum transfer unit,最大传输单位)指定一个传输帧的最大长度。网络层的协议必须遵守该值的限制,可能需要将分组拆分为更小的单位 |
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| [type](http://lxr.free-electrons.com/source/include/linux/netdevice.h?v=4.7#L1692) | 保存设备的硬件类型,它使用的是 <if_arp.h> 中定义的常数.<br>例如, ARPHRD_ETHER和ARPHDR_IEEE802 分别表示10兆以太网和802.2以太网, ARPHRD_APPLETLK 表示AppleTalk,而ARPHRD_LOOPBACK 表示环回设备 |
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| [dev_addr](http://lxr.free-electrons.com/source/include/linux/netdevice.h?v=4.7#L1701) | 存储设备的硬件地址(如以太网卡的MAC地址),而 addr_len 指定该地址的长度 |
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| broadcast | 是用于向附接的所有站点发送消息的广播地址 |
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||||
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||||
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||||
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||||
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ip_ptr 、 ip6_ptr 、 atalk_ptr 等指针指向特定于协议的数据,通用代码不会操作这些数据, 他们定义在[include/linux/netdevice.h?v=4.7, line 1721](http://lxr.free-electrons.com/source/include/linux/netdevice.h?v=4.7#L1721)
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||||
|
||||
```cpp
|
||||
struct net_device
|
||||
{
|
||||
/* Protocol-specific pointers */
|
||||
#if IS_ENABLED(CONFIG_VLAN_8021Q)
|
||||
struct vlan_info __rcu *vlan_info;
|
||||
#endif
|
||||
#if IS_ENABLED(CONFIG_NET_DSA)
|
||||
struct dsa_switch_tree *dsa_ptr;
|
||||
#endif
|
||||
#if IS_ENABLED(CONFIG_TIPC)
|
||||
struct tipc_bearer __rcu *tipc_ptr;
|
||||
#endif
|
||||
void *atalk_ptr;
|
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struct in_device __rcu *ip_ptr;
|
||||
struct dn_dev __rcu *dn_ptr;
|
||||
struct inet6_dev __rcu *ip6_ptr;
|
||||
void *ax25_ptr;
|
||||
struct wireless_dev *ieee80211_ptr;
|
||||
struct wpan_dev *ieee802154_ptr;
|
||||
#if IS_ENABLED(CONFIG_MPLS_ROUTING)
|
||||
struct mpls_dev __rcu *mpls_ptr;
|
||||
#endif
|
||||
};
|
||||
```
|
||||
|
||||
|
||||
##2.2 函数指针操作接口
|
||||
-------
|
||||
|
||||
`net_device`结构的大多数成员都是函数指针,执行与网卡相关的典型任务. 尽管不同适配器的实现各有不同,但调用的语法(和执行的任务)总是相同的. 因而这些成员表示了与下一个协议层次的抽象接口. 这些接口使得内核能够用同一组接口函数来访问所有的网卡, 而网卡的驱动程序负责实现细节.
|
||||
|
||||
###2.2.1 net_device中的函数指针成员
|
||||
-------
|
||||
|
||||
|
||||
```cpp
|
||||
// http://lxr.free-electrons.com/source/include/linux/netdevice.h#L1668
|
||||
struct net_device
|
||||
{
|
||||
const struct net_device_ops *netdev_ops;
|
||||
const struct ethtool_ops *ethtool_ops;
|
||||
#ifdef CONFIG_NET_SWITCHDEV
|
||||
const struct switchdev_ops *switchdev_ops;
|
||||
#endif
|
||||
#ifdef CONFIG_NET_L3_MASTER_DEV
|
||||
const struct l3mdev_ops *l3mdev_ops;
|
||||
#endif
|
||||
|
||||
const struct header_ops *header_ops;
|
||||
};
|
||||
```
|
||||
|
||||
###2.2.2 net_device_ops基本函数操作
|
||||
-------
|
||||
|
||||
|
||||
|
||||
其中`net_device_ops`函数中提供了最基本的`net_device`操作接口, 这些函数指针成员变量的命名都以`ndo_`开头, 定义在[`include/linux/netdevice.h, line 1104`](http://lxr.free-electrons.com/source/include/linux/netdevice.h#L1104)
|
||||
|
||||
|
||||
|
||||
| 函数 | 描述 |
|
||||
|:---:|:----:|
|
||||
| ndo_open 和 ndo_stop | 分别初始化和终止网卡。这些操作通常在内核外部通过调用ifconfig命令触发<br>open负责初始化硬件寄存器并注册系统资源,如中断、DMA、IO端口等<br> close 释放这些资源,并停止传输 |
|
||||
| ndo_start_xmit | 用于从等待队列删除已经完成的分组并将其发送出去 |
|
||||
| ndo_get_stats | 查询统计数据,并将数据封装到一个类型为`net_device_stats`的结构中返回. 该结构的成员有20多个, 都是一些数值, 如发送、接收、出错、丢弃的分组的数目等. (统计学爱好者可用 ifconfig 和 netstat -i 查询这些数据)<br>因为`net_device`结构没有提供存储`net_device_stats`对象的专用字段,各个设备驱动程序必须在私有数据区保存该对象 |
|
||||
| ndo_tx_timeout | 调用`tx_timeout`来解决分组传输失败的问题 |
|
||||
| ndo_do_ioctl |将特定于设备的命令发送到网卡。
|
||||
| ndo_change_mtu | 是由`eth_change_mtu`实现的,负责修改最大传输单位. 以太网的默认值是1.5KB, 其他传输技术各有不同的默认值. 在某些情况下, 增大/减小该值是有用的. 但许多网卡不允许这样做,只支持默认的硬件设置 |
|
||||
|
||||
有些函数通常不是由特定于驱动程序的代码来实现的,它们对所有的以太网卡都是相同的. 因而内核提供了默认实现(在 [`net/ethernet/eth.c`](http://lxr.free-electrons.com/source/net/ethernet/eth.c?v=4.7)中)
|
||||
|
||||
|
||||
|
||||
可以将一个ioctl应用到套接字的文件描述符, 从用户空间修改对应的网络设备的配置. 必须指定`sockios.h`中定义的某个符号常数, 表明修改配置的哪一部分. 例如, SIOCGIFHWADDR负责设置网卡的硬件地址, 内核最终将该任务委派给`net_device`实例的`set_mac_address`函数. 设备相关的常数会传递给`do_ioctl`函数处理. 由于有许多调节选项,具体的实现非常冗长,我们对此也不是特别感兴趣,就不在这里讨论了.
|
||||
|
||||
网络设备分两个方向工作, 即发送和接收(这两个方向通常称为下向流和上向流). 内核源代码包含了两个驱动程序框架( `drivers/net`中的`isa-skeleton.c`和`pci-skeleton.c`), 可用作网络驱动程序的模板. 在下文中, 主要关注驱动程序与硬件的交互, 但又不想局限于某种特定的专有网卡类型时, 偶尔会引用这两个驱动程序. 与对硬件进行编程相比,我们对内核与硬件通信所用的接口更感兴趣, 这也是我们在下文详细介绍这些接口的原因. 下面将介绍如何将网络设备注册到内核中.
|
||||
|
||||
|
||||
|
||||
###2.2.3 header_ops
|
||||
-------
|
||||
|
||||
|
||||
|
||||
`net_device->header_ops`数接口对象是一个指向`struct header_ops`构的指针,该结构提供了更多的函数指针, 用于操作硬件首部. 该结构定义在[`include/linux/netdevice.h?V=4.7, line 261`](http://lxr.free-electrons.com/source/include/linux/netdevice.h?V=4.7#L261)
|
||||
|
||||
```cpp
|
||||
struct header_ops {
|
||||
int (*create) (struct sk_buff *skb, struct net_device *dev,
|
||||
unsigned short type, const void *daddr,
|
||||
const void *saddr, unsigned int len);
|
||||
int (*parse)(const struct sk_buff *skb, unsigned char *haddr);
|
||||
int (*cache)(const struct neighbour *neigh, struct hh_cache *hh, __be16 type);
|
||||
void (*cache_update)(struct hh_cache *hh,
|
||||
const struct net_device *dev,
|
||||
const unsigned char *haddr);
|
||||
bool (*validate)(const char *ll_header, unsigned int len);
|
||||
};
|
||||
|
||||
```
|
||||
|
||||
|
||||
其中最重要的是`header_ops->create`和`header_ops->parse`, 前者创建一个新的硬件首部, 后者分析一个给定的硬件首部
|
||||
|
||||
* header_ops->create 的默认实现是`eth_header`该函数为现存的分组数据生成网络访问层首部.
|
||||
|
||||
* header_ops->parse(通常由eth_header_parse实现)获取给定的分组的源硬件地址.
|
||||
|
||||
##2.2 注册网络设备
|
||||
-------
|
||||
|
||||
每个网络设备都按照如下过程注册.
|
||||
|
||||
1. `alloc_netdev`分配一个新的`struct net_device`实例,一个特定于协议的函数用典型值填充该结构。对于以太网设备,该函数是`ether_setup`. 其他的协议(这里不详细介绍)会使用形如`XXX_setup`的函数, 其中 XXX可以是`fddi(fiber distributed data interface`, 光纤分布式数据接口)、tr
|
||||
(`token ring`,令牌环网)、 `ltalk`(指`Apple LocalTalk`)、 `hippi`(`high-performance parallel interface`, 高性能并行接口)或`fc` (`fiber channel`, 光纤通道)
|
||||
|
||||
内核中的一些伪设备在不绑定到硬件的情况下实现了特定的接口,它们也使用了`net_device`框架. 例如, ppp_setup 根据PPP协议初始化设备。内核源代码中还可以找到几个 XXX_setup 函数
|
||||
|
||||
2. 在`struct net_device`填充完毕后, 需要用 `register_netdev`或`register_netdevice`注册.
|
||||
这两个函数的区别在于, `register_netdev`可处理用作 接口名称的格式串(有限). 在`net_device->dev`中给出的名称可以包含格式说明符%d. 在设备注册时, 内核会选择一个唯一的数字来代替%d.
|
||||
例如, 以太网设备可以指定`eth%d`, 而内核随后会创建设备eth0、eth1 ......
|
||||
|
||||
|
||||
便捷函数`alloc_etherdev(sizeof_priv)`分配一个`struct net_device`实例, 外加`sizeof_priv`字节私有数据区. 回想前文可知, `net_device->priv`是一个指针, 指向与设备相关联的特定于驱动程序的数据. 此外, 还调用了上面提到的`ether_setup`来设置特定于以太网的标准值.
|
||||
|
||||
`register_netdevice`的各个处理步骤概括为图12-9中的代码流程图
|
||||
|
||||
|
||||
|
||||
|
||||
如果`net_device->init`提供了特定于设备的初始化函数,那么内核在进一步处理之前, 将先调用该函数.
|
||||
|
||||
由`dev_new_index`生成在所属命名空间中唯一标识该设备的接口索引。该索引保存在 net_device->ifindex`中. 在确保所选择的名称尚未使用, 而且没有指定自相矛盾的设备特性(所支持特性的列表, 请参见`<netdevice.h>`中的 NETIF_F_* )后, 用`netdev_register_kobject`将新设备添加到通用内核对象模型中. 该函数还会创建上文提到的sysfs项. 最后,该设备集成到特定命名空间的链表中, 以及以设备名和接口索引为散列键的两个散列表中.
|
||||
|
||||
|
||||
@@ -1,21 +0,0 @@
|
||||
进程虚拟地址空间
|
||||
=======
|
||||
|
||||
| 日期 | 内核版本 | 架构| 作者 | GitHub| CSDN |
|
||||
| ------- |:-------:|:-------:|:-------:|:-------:|:-------:|
|
||||
| 2016-06-14 | [Linux-4.7](http://lxr.free-electrons.com/source/?v=4.7) | X86 & arm | [gatieme](http://blog.csdn.net/gatieme) | [LinuxDeviceDrivers](https://github.com/gatieme/LDD-LinuxDeviceDrivers) | [Linux内存管理](http://blog.csdn.net/gatieme/article/category/6225543) |
|
||||
|
||||
|
||||
#1 网络访问层
|
||||
-------
|
||||
|
||||
前面讲述了Linux内核中网络子系统的结构, 现在我们把注意力转向**网络实现的第一层, 即网络访问层**. 该层主要负责在计算机之间传输信息，与网卡的设备驱动程序直接协作.
|
||||
|
||||
本节不会讨论网卡驱动程序的实现和相关的问题, 因为其中采用的方法与第6章的描述仅稍有不同. 本节将详细介绍由各个网卡驱动程序提供、由网络实现代码使用的接口，它们提供了硬件的抽象视图.
|
||||
|
||||
这里根据以太网帧来解释如何在"线上"(on the cable)表示数据，并描述接收到一个分组之后, 将该分组传递到更高层之前，需要完成哪些步骤.
|
||||
|
||||
#2 网络设备的表示
|
||||
-------
|
||||
|
||||
在内核中, 每个网络设备都表示为net_device结构的一个实例。在分配并填充该结构的一个实例之后，必须用net/core/dev.c中的register_netdev函数将其注册到内核。该函数完成一些初始化任务，并将该设备注册到通用设备机制内。这会创建一个sysfs项（参见10.3节）/sys/class/net/<device>，关联到该设备对应的目录。如果系统包含一个PCI网卡和一个环回接口设备，则在
|
||||
@@ -0,0 +1,93 @@
|
||||
进程虚拟地址空间
|
||||
=======
|
||||
|
||||
| 日期 | 内核版本 | 架构| 作者 | GitHub| CSDN |
|
||||
| ------- |:-------:|:-------:|:-------:|:-------:|:-------:|
|
||||
| 2016-06-14 | [Linux-4.7](http://lxr.free-electrons.com/source/?v=4.7) | X86 & arm | [gatieme](http://blog.csdn.net/gatieme) | [LinuxDeviceDrivers](https://github.com/gatieme/LDD-LinuxDeviceDrivers) | [Linux内存管理](http://blog.csdn.net/gatieme/article/category/6225543) |
|
||||
|
||||
|
||||
#2 接受分组
|
||||
-------
|
||||
|
||||
|
||||
分组到达内核的时间是不可预测的. 所有现代的设备驱动程序都使用中断来通知内核(或系统)有分组到达. 网络驱动程序对特定于设备的中断设置了一个处理例程, 因此每当该中断被引发时(即分组到达), 内核都调用该处理程序, 将数据从网卡传输到物理内存, 或通知内核在一定时间后进行处理.
|
||||
|
||||
几乎所有的网卡都支持DMA模式, 能够自行将数据传输到物理内存. 但这些数据仍然需要解释和处理,这在稍后进行.
|
||||
|
||||
##2.1 传统方法
|
||||
-------
|
||||
|
||||
当前, 内核为分组的接收提供了两个框架. 其中一个很早以前就集成到内核中了, 因而称为传统方法. 但与超高速网络适配器协作时, 该API会出现问题,因而网络子系统的开发者已经设计了一种新的API(通常称为NAPI 1). 我们首先从传统方法开始, 因为它比较易于理解. 另外, 使用旧API的适配器较多, 而使用新API的较少. 这没有问题, 因为其物理传输速度没那么高, 不需要新方法. NAPI在稍后讨论
|
||||
|
||||
图12-10给出了在一个分组到达网络适配器之后,该分组穿过内核到达网络层函数的路径
|
||||
|
||||
|
||||
因为分组是在中断上下文中接收到的, 所以处理例程只能执行一些基本的任务,避免系统(或当前CPU)的其他任务延迟太长时间.
|
||||
|
||||
在中断上下文中, 数据由3个短函数2处理, 执行了下列任务.
|
||||
|
||||
![接收到的分组穿过内核的路径]()
|
||||
|
||||
|
||||
1. net_interrupt是由设备驱动程序设置的中断处理程序. 它将确定该中断是否真的是由接收到的分组引发的(也存在其他的可能性, 例如, 报告错误或确认某些适配器执行的传输任务). 如果确实如此,则控制将转移到`net_rx`.
|
||||
|
||||
2. `net_rx`函数也是特定于网卡的, 首先创建一个新的套接字缓冲区. 分组的内容接下来从网卡传输到缓冲区(也就是进入了物理内存), 然后使用内核源代码中针对各种传输类型的库函数来分析首部数据. 这项分析将确定分组数据所使用的网络层协议,例如IP协议.
|
||||
|
||||
3. 与上述两个方法不同, `netif_rx`函数不是特定于网络驱动程序的,该函数位于`net/core/dev.c`. 调用该函数,标志着控制由特定于网卡的代码转移到了网络层的通用接口部分.
|
||||
|
||||
该函数的作用在于, 将接收到的分组放置到一个特定于CPU的等待队列上, 并退出中断上下文, 使得CPU可以执行其他任务.
|
||||
|
||||
内核在全局定义的softnet_data数组中管理进出分组的等待队列, 数组项类型为softnet_data. 为提高多处理器系统的性能, 对每个CPU都会创建等待队列, 支持分组的并行处理.
|
||||
|
||||
不心使用显式的锁机制来保护等待队列免受并发访问, 因为每个CPU都只修改自身的队列, 不会干扰其他CPU的工作. 下文将忽略多处理器相关内容, 只考虑单"softnet_data等待队列", 避免过度复杂化.
|
||||
|
||||
目前只对该数据结构的一个成员感兴趣:
|
||||
|
||||
```cpp
|
||||
<netdevice.h>
|
||||
struct softnet_data
|
||||
{
|
||||
...
|
||||
struct sk_buff_head input_pkt_queue;
|
||||
...
|
||||
};
|
||||
```
|
||||
|
||||
`input_pkt_queue`使用上文提到的`sk_buff_head`表头, 对所有进入的分组建立一个链表.
|
||||
|
||||
`netif_rx`在结束工作之前将软中断`NET_RX_SOFTIRQ`标记为即将执行, 然后退出中断上下文.
|
||||
|
||||
`net_rx_action`用作该软中断的处理程序. 其代码流程图在图12-11给出. 请记住, 这里描述的是一个简化的版本. 完整版包含了对高速网络适配器引入的新方法, 将在下文介绍.
|
||||
|
||||
|
||||
![图12-11 net_rx_action 的代码流程图]()
|
||||
|
||||
|
||||
在一些准备任务之后,工作转移到`process_backlog`, 该函数在循环中执行下列步骤. 为简化描述, 假定循环一直进行, 直至所有的待决分组都处理完成,不会被其他情况中断.
|
||||
|
||||
1. `__skb_dequeue`从等待队列移除一个套接字缓冲区, 该缓冲区管理着一个接收到的分组.
|
||||
|
||||
2. 由`netif_receive_skb`函数分析分组类型, 以便根据分组类型将分组传递给网络层的接收函数(即传递到网络系统的更高一层). 为此, 该函数遍历所有可能负责当前分组类型的所有网络层函数, 一一调用`deliver_skb`.
|
||||
|
||||
接下来`deliver_skb`函数使用一个特定于分组类型的处理程序`func`, 承担对分组的更高层(例如互联网络层)的处理.
|
||||
|
||||
`netif_receive_skb`也处理诸如桥接之类的专门特性, 但讨论这些边角情况是不必要的, 至少在平均水准的系统中, 此类特性都属于边缘情况.
|
||||
|
||||
所有用于从底层的网络访问层接收数据的网络层函数都注册在一个散列表中, 通过全局数组`ptype_base`实现.
|
||||
|
||||
新的协议通过`dev_add_pack`增加. 各个数组项的类型为`struct packet_type`, 定义如下:
|
||||
|
||||
```cpp
|
||||
<netdevice.h>
|
||||
struct packet_type {
|
||||
__be16
|
||||
struct net_device
|
||||
int
|
||||
```
|
||||
|
||||
type 指定了协议的标识符,处理程序会使用该标识符。 dev 将一个协议处理程序绑定到特定的网卡
|
||||
( NULL 指针表示该处理程序对系统中所有网络设备都有效)
|
||||
。
|
||||
func 是该结构的主要成员。它是一个指向网络层函数的指针,如果分组的类型适当,将其传递给
|
||||
该函数。其中一个处理程序就是 ip_rcv ,用于基于IPv4的协议,在下文讨论。
|
||||
netif_receive_skb 对给定的套接字缓冲区查找适当的处理
|
||||
@@ -0,0 +1,260 @@
|
||||
struct net_device {
|
||||
char name[IFNAMSIZ];
|
||||
struct hlist_node name_hlist;
|
||||
char *ifalias;
|
||||
/*
|
||||
* I/O specific fields
|
||||
* FIXME: Merge these and struct ifmap into one
|
||||
*/
|
||||
unsigned long mem_end;
|
||||
unsigned long mem_start;
|
||||
unsigned long base_addr;
|
||||
int irq;
|
||||
|
||||
atomic_t carrier_changes;
|
||||
|
||||
/*
|
||||
* Some hardware also needs these fields (state,dev_list,
|
||||
* napi_list,unreg_list,close_list) but they are not
|
||||
* part of the usual set specified in Space.c.
|
||||
*/
|
||||
|
||||
unsigned long state;
|
||||
|
||||
struct list_head dev_list;
|
||||
struct list_head napi_list;
|
||||
struct list_head unreg_list;
|
||||
struct list_head close_list;
|
||||
struct list_head ptype_all;
|
||||
struct list_head ptype_specific;
|
||||
|
||||
struct {
|
||||
struct list_head upper;
|
||||
struct list_head lower;
|
||||
} adj_list;
|
||||
|
||||
struct {
|
||||
struct list_head upper;
|
||||
struct list_head lower;
|
||||
} all_adj_list;
|
||||
|
||||
netdev_features_t features;
|
||||
netdev_features_t hw_features;
|
||||
netdev_features_t wanted_features;
|
||||
netdev_features_t vlan_features;
|
||||
netdev_features_t hw_enc_features;
|
||||
netdev_features_t mpls_features;
|
||||
netdev_features_t gso_partial_features;
|
||||
|
||||
int ifindex;
|
||||
int group;
|
||||
|
||||
struct net_device_stats stats;
|
||||
|
||||
atomic_long_t rx_dropped;
|
||||
atomic_long_t tx_dropped;
|
||||
atomic_long_t rx_nohandler;
|
||||
|
||||
#ifdef CONFIG_WIRELESS_EXT
|
||||
const struct iw_handler_def *wireless_handlers;
|
||||
struct iw_public_data *wireless_data;
|
||||
#endif
|
||||
const struct net_device_ops *netdev_ops;
|
||||
const struct ethtool_ops *ethtool_ops;
|
||||
#ifdef CONFIG_NET_SWITCHDEV
|
||||
const struct switchdev_ops *switchdev_ops;
|
||||
#endif
|
||||
#ifdef CONFIG_NET_L3_MASTER_DEV
|
||||
const struct l3mdev_ops *l3mdev_ops;
|
||||
#endif
|
||||
|
||||
const struct header_ops *header_ops;
|
||||
|
||||
unsigned int flags;
|
||||
unsigned int priv_flags;
|
||||
|
||||
unsigned short gflags;
|
||||
unsigned short padded;
|
||||
|
||||
unsigned char operstate;
|
||||
unsigned char link_mode;
|
||||
|
||||
unsigned char if_port;
|
||||
unsigned char dma;
|
||||
|
||||
unsigned int mtu;
|
||||
unsigned short type;
|
||||
unsigned short hard_header_len;
|
||||
|
||||
unsigned short needed_headroom;
|
||||
unsigned short needed_tailroom;
|
||||
|
||||
/* Interface address info. */
|
||||
unsigned char perm_addr[MAX_ADDR_LEN];
|
||||
unsigned char addr_assign_type;
|
||||
unsigned char addr_len;
|
||||
unsigned short neigh_priv_len;
|
||||
unsigned short dev_id;
|
||||
unsigned short dev_port;
|
||||
spinlock_t addr_list_lock;
|
||||
unsigned char name_assign_type;
|
||||
bool uc_promisc;
|
||||
struct netdev_hw_addr_list uc;
|
||||
struct netdev_hw_addr_list mc;
|
||||
struct netdev_hw_addr_list dev_addrs;
|
||||
|
||||
#ifdef CONFIG_SYSFS
|
||||
struct kset *queues_kset;
|
||||
#endif
|
||||
unsigned int promiscuity;
|
||||
unsigned int allmulti;
|
||||
|
||||
|
||||
/* Protocol-specific pointers */
|
||||
|
||||
#if IS_ENABLED(CONFIG_VLAN_8021Q)
|
||||
struct vlan_info __rcu *vlan_info;
|
||||
#endif
|
||||
#if IS_ENABLED(CONFIG_NET_DSA)
|
||||
struct dsa_switch_tree *dsa_ptr;
|
||||
#endif
|
||||
#if IS_ENABLED(CONFIG_TIPC)
|
||||
struct tipc_bearer __rcu *tipc_ptr;
|
||||
#endif
|
||||
void *atalk_ptr;
|
||||
struct in_device __rcu *ip_ptr;
|
||||
struct dn_dev __rcu *dn_ptr;
|
||||
struct inet6_dev __rcu *ip6_ptr;
|
||||
void *ax25_ptr;
|
||||
struct wireless_dev *ieee80211_ptr;
|
||||
struct wpan_dev *ieee802154_ptr;
|
||||
#if IS_ENABLED(CONFIG_MPLS_ROUTING)
|
||||
struct mpls_dev __rcu *mpls_ptr;
|
||||
#endif
|
||||
|
||||
/*
|
||||
* Cache lines mostly used on receive path (including eth_type_trans())
|
||||
*/
|
||||
unsigned long last_rx;
|
||||
|
||||
/* Interface address info used in eth_type_trans() */
|
||||
unsigned char *dev_addr;
|
||||
|
||||
#ifdef CONFIG_SYSFS
|
||||
struct netdev_rx_queue *_rx;
|
||||
|
||||
unsigned int num_rx_queues;
|
||||
unsigned int real_num_rx_queues;
|
||||
#endif
|
||||
|
||||
unsigned long gro_flush_timeout;
|
||||
rx_handler_func_t __rcu *rx_handler;
|
||||
void __rcu *rx_handler_data;
|
||||
|
||||
#ifdef CONFIG_NET_CLS_ACT
|
||||
struct tcf_proto __rcu *ingress_cl_list;
|
||||
#endif
|
||||
struct netdev_queue __rcu *ingress_queue;
|
||||
#ifdef CONFIG_NETFILTER_INGRESS
|
||||
struct list_head nf_hooks_ingress;
|
||||
#endif
|
||||
|
||||
unsigned char broadcast[MAX_ADDR_LEN];
|
||||
#ifdef CONFIG_RFS_ACCEL
|
||||
struct cpu_rmap *rx_cpu_rmap;
|
||||
#endif
|
||||
struct hlist_node index_hlist;
|
||||
|
||||
/*
|
||||
* Cache lines mostly used on transmit path
|
||||
*/
|
||||
struct netdev_queue *_tx ____cacheline_aligned_in_smp;
|
||||
unsigned int num_tx_queues;
|
||||
unsigned int real_num_tx_queues;
|
||||
struct Qdisc *qdisc;
|
||||
unsigned long tx_queue_len;
|
||||
spinlock_t tx_global_lock;
|
||||
int watchdog_timeo;
|
||||
|
||||
#ifdef CONFIG_XPS
|
||||
struct xps_dev_maps __rcu *xps_maps;
|
||||
#endif
|
||||
#ifdef CONFIG_NET_CLS_ACT
|
||||
struct tcf_proto __rcu *egress_cl_list;
|
||||
#endif
|
||||
#ifdef CONFIG_NET_SWITCHDEV
|
||||
u32 offload_fwd_mark;
|
||||
#endif
|
||||
|
||||
/* These may be needed for future network-power-down code. */
|
||||
struct timer_list watchdog_timer;
|
||||
|
||||
int __percpu *pcpu_refcnt;
|
||||
struct list_head todo_list;
|
||||
|
||||
struct list_head link_watch_list;
|
||||
|
||||
enum { NETREG_UNINITIALIZED=0,
|
||||
NETREG_REGISTERED, /* completed register_netdevice */
|
||||
NETREG_UNREGISTERING, /* called unregister_netdevice */
|
||||
NETREG_UNREGISTERED, /* completed unregister todo */
|
||||
NETREG_RELEASED, /* called free_netdev */
|
||||
NETREG_DUMMY, /* dummy device for NAPI poll */
|
||||
} reg_state:8;
|
||||
|
||||
bool dismantle;
|
||||
|
||||
enum {
|
||||
RTNL_LINK_INITIALIZED,
|
||||
RTNL_LINK_INITIALIZING,
|
||||
} rtnl_link_state:16;
|
||||
|
||||
void (*destructor)(struct net_device *dev);
|
||||
|
||||
#ifdef CONFIG_NETPOLL
|
||||
struct netpoll_info __rcu *npinfo;
|
||||
#endif
|
||||
|
||||
possible_net_t nd_net;
|
||||
|
||||
/* mid-layer private */
|
||||
union {
|
||||
void *ml_priv;
|
||||
struct pcpu_lstats __percpu *lstats;
|
||||
struct pcpu_sw_netstats __percpu *tstats;
|
||||
struct pcpu_dstats __percpu *dstats;
|
||||
struct pcpu_vstats __percpu *vstats;
|
||||
};
|
||||
|
||||
struct garp_port __rcu *garp_port;
|
||||
struct mrp_port __rcu *mrp_port;
|
||||
|
||||
struct device dev;
|
||||
const struct attribute_group *sysfs_groups[4];
|
||||
const struct attribute_group *sysfs_rx_queue_group;
|
||||
|
||||
const struct rtnl_link_ops *rtnl_link_ops;
|
||||
|
||||
/* for setting kernel sock attribute on TCP connection setup */
|
||||
#define GSO_MAX_SIZE 65536
|
||||
unsigned int gso_max_size;
|
||||
#define GSO_MAX_SEGS 65535
|
||||
u16 gso_max_segs;
|
||||
|
||||
#ifdef CONFIG_DCB
|
||||
const struct dcbnl_rtnl_ops *dcbnl_ops;
|
||||
#endif
|
||||
u8 num_tc;
|
||||
struct netdev_tc_txq tc_to_txq[TC_MAX_QUEUE];
|
||||
u8 prio_tc_map[TC_BITMASK + 1];
|
||||
|
||||
#if IS_ENABLED(CONFIG_FCOE)
|
||||
unsigned int fcoe_ddp_xid;
|
||||
#endif
|
||||
#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)
|
||||
struct netprio_map __rcu *priomap;
|
||||
#endif
|
||||
struct phy_device *phydev;
|
||||
struct lock_class_key *qdisc_tx_busylock;
|
||||
bool proto_down;
|
||||
};
|
||||
Binary file not shown.
|
After Width: | Height: | Size: 51 KiB |
Reference in New Issue
Block a user